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github-actions edited this page Nov 30, 2023 · 2 revisions

Controller state machine

In this file we will document how the VPN Controller works. But in the meantime, we just have a diagram about how the ServerData object is cached to avoid race conditions with the rest of the app.

Activation flow

  • m_serverData is a copy of the location, taken when the user (or something else) triggers a VPN activation. This value is kept constant for the whole duration of the operation. If something happens, this and MozillaVPN::serverData are in sync.
  • If there is a server-switch request while an activation is in progress, we start a disconnect operation and we store the new location in m_nextServerData.

See this flow:

sequenceDiagram
    User->>Client: Location X is set
    User->>Client: VPN activation request
    activate Client
    Client->>Client: Task scheduled (copy of location is taken: Xc = X)
    deactivate Client
    Client->>Controller: Task run: activate (Xc)
    activate Controller
    Controller->>Controller: m_serverData = Xc
    Controller->>Controller: Connecting...
    User->>Client: Location Y is set
    activate Client
    Client->>Client: Task scheduled (copy of location is taken: Yc = Y)
    deactivate Client
    Controller->>Controller: Conferming...
    Client->>Controller: Task run: serverSwitch (Yc)
    Controller->>Controller: m_nextServerData = Yc
    Controller->>Controller: Connected
    Controller->>Controller: deactivate...
    Controller->>Controller: activate(m_nextServerData)
    Controller->>Controller: m_serverData = m_nextServerData
    deactivate Controller
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